Unbalanced circuits such as coaxial cable and radio-frequency amplifiers are generally preferred for simplicity and economy. But for increased performance, balanced circuits are sometimes desirable. A rather critical stage in a conventional radio receiver, for example, is a radio frequency mixer that converts a selected radio frequency to a fixed intermediate frequency. The ability of the radio receiver to reject intermodulation interference, for example, is primarily a function of the performance of the radio frequency mixer. In the ideal case, the mixer multiplies radio frequency signals by a local oscillator signal to produce corresponding intermediate frequency signals. In practice the mixer also multiplies or "mixes" the radio frequency signals among themselves to obtain some level of interfering signal at the intermediate frequency.
Mixers having close to ideal performance are known as "balanced" mixers. Balanced mixers use balanced signals which are fed through non-linear components and then combined to provided cancellation of certain undesired signals. In particular, it is possible to cancel the fundamental and odd-order intermodulation components. Balanced mixers, however, typically require at least one balance transformer. The balanced transformer typically includes windings on a toroidal ferrite core. The winding of such a transformer is therefore a relative expensive operation. Also, the assembly of such a transformer onto a circuit board or substrate involves additional cost. For economy, the transformer leads are provided by the ends of the wires forming the transformer's windings which require hand insertion and soldering to the circuit board, with careful attention to dressing of the leads to maintain balance of the signals. The tranformers is then secured to the circuit board by applying cement.
To avoid the costs associated with the fabrication and assembly of the balanced transformer , it would be desirable to manufacture the balanced transformer as part of the printed circuit itself.